RESUMO
Akkermansia muciniphila is considered a next-generation probiotic because of its immense potential to regulate disorders. We isolated 31 strains of A. muciniphila from feces or breast milk of healthy people. After genome sequencing, assembly, and analysis, we selected six strains (AM01 to AM06) for further exploration. We first analyzed their general characteristics, including morphological description, growth characteristics, and physiological and biochemical characteristics, and then confirmed their genetic characteristics, including GC content, putative virulence factors, and antibiotic resistance genes. We next investigated the tolerance of these strains to artificial gastric and intestinal fluids and bile salts to evaluate their survival potential in the digestive tract. Drug sensitivity tests were also conducted based on the analysis of the antibiotic resistance genes of these strains. Furthermore, we examined the genetic stability and acute toxicity of two strains (AM02 and AM06) in mice. Finally, the safety of AM06 was evaluated in normal mice and nude mice. AM06 exhibited adaptability to pH changes. Since AM02 and AM03 showed more resistance to antibiotics than AM01 and AM04 to AM06, their potential clinical application may be limited. Both AM02 and AM06 were genetically and phenotypically stable and safe in normal mice, and AM06 was safe in nude mice. Considering all this together, AM06 is a safe A. muciniphila strain and exhibits a great potential for use as a probiotic strain among the isolated strains. IMPORTANCE In this study, we isolated 30 strains of Akkermansia muciniphila from different samples of human feces, and for the first time we isolated an A. muciniphila strain from human breast milk. This isolation verified the existence of microbes in human breast milk, which suggests that A. muciniphila can be vertically propagated from mother to infant and participates in the formation of the early gut microbiome. We then systematically evaluated the potential for use as a probiotic of this A. muciniphila strains according to the FAO/WHO recommendation. We confirmed that the AM06 strain isolated from breast milk has no virulence factors and is genetically stable and nonpathogenic for both normal mice and nude mice. Moreover, its tolerance to pH changes and bile salts indicates its desirable probiotic properties. Thus, we propose that the AM06 strain of A. muciniphila is safe for use as a probiotic candidate.
RESUMO
The prominent human symbiont Bacteroides fragilis protects animals from intestinal diseases, such as ulcerative colitis, and its capsular polysaccharide plays a key role in reducing inflammation. B. fragilis strain ZY-312 was isolated from the feces of a healthy breast-fed infant, and the zwitterionic capsular polysaccharide zwitterionic polysaccharide, TP2, was extracted. In rats with 2,4-dinitrobenzenesulfonic acid (DNBS)-induced enteritis, TP2 at an optimal dose of 2.5 mg/kg could significantly alleviate enteritis and reduced the degree of intestinal adhesions, the intestinal ulcer area, and the incidence of ulcers in rats. To understand the underlying mechanism, TP2 was labeled with Fluorescein isothiocyanate and orally administered at a dose of 2.5 mg/kg in rats. TP2 was mainly distributed in the cecum and colorectum, but it was not detected in the blood and other organs except that a compound with a molecular weight greater than that of TP2-FITC was found in liver tissue. During the absorption, distribution, metabolism, and excretion, TP2 was indigestible. These results were further confirmed by investigation in the simulated gastric, intestinal fluid, and colonic fluid with fecal microbiota in vitro, where TP2 remained unaltered at different time points. Furthermore, flora composition was analyzed in simulated colonic fluid with TP2 added and it was found that TP2 increased the abundance of Faecalibacterium, Enterococcus romboutsia, and Ruminococcaceae, whereas the abundance of the phylum Proteobacteria represented by Sutterella, Desulfovibrio, and Enterobacteriaceae was decreased. However, the amount of short-chain fatty acids in the simulated colonic fluid was not changed by intestinal flora post-TP2 addition. In conclusion, these findings confirmed that TP2, a capsular polysaccharide of B. fragilis, protects against ulcerative colitis in an undegraded form.